Copper tolerant Elsholtzia splendens facilitates Commelina communis on a copper mine spoil

Background and aims There is evidence that plant facilitation occurs in heavy metal wastelands, but the extent and mechanisms of facilitation are not known. The copper (Cu) tolerant Elsholtzia splendens is a dominant pioneer species during the secondary succession on copper mine spoils in eastern China. Species appearing later are often associated with patches of E. splendens . We hypothesize that E. splendens facilitates neighbors by modifying local soil properties. Methods We conducted a field study on a heavy metal wasteland with local variation in soil Cu level to investigate the performance of a target species, Commelina communis , growing in open gaps vs. growing with E. splendens . Soil physicochemical and biological properties, biomass, plant interaction intensity as well as heavy metal concentration in C. communis were measured to study the effects of the presence of E. splendens . Results Effects of the presence of E. splendens on C. communis were generally positive, but negative effects were sometimes observed. Positive effects of E. splendens increased with increasing soil Cu level. Soil microbial activity was higher in the presence of E. splendens . Our results are consistent with the hypothesis that facilitation occurred through enrichment of the microbial properties of the soil, especially soil respiration rate and enzyme activity. Conclusions Our study highlights the importance of soil-mediated plant-plant interactions for the establishment of C. communis on heavy metal-contaminated sites. These interactions are important for the restoration of heavy metal wastelands.